Electricity Flashcards
State what is meant by an alternating current
a.c. is a current which changes direction and instantaneous value with time.
How do you determine the peak voltage from an oscilloscope?
Vpeak = number of divisions X y gain
State what is meant by a direct current
d.c. is a current that does not change direction or instantaneous value with time.
Sketch a graph of current vs time for a discharging capacitor
Discharging capacitor graph current vs time
Describe the effect of changing resistance on the charging and discharging curves for a capacitor?
Increasing resistance increases discharge time
State what is meant by the short circuit current
The current drawn from a supply when the terminals are connected together with no load resistance. This can produce a large current and can be dangerous.
I = E/r
What is a p-n junction?
A p-n junction is an interface or a boundary between two semiconductor material types, namely the p-type and the n-type, inside a semiconductor. The p-side or the positive side of the semiconductor has an excess of holes and the n-side or the negative side has an excess of electrons.
Describe experiments to measure the current and voltage for charging and discharging capacitors
A = Discharging B = charging
Measure the current and voltage at regular intervals using the voltmeter and ammeter
What are the rules for a parallel circuit?
Is = I1 + I2… (splits at branches)
Vs=V1 =V2 =……
1/RT = 1/R1 + 1/R2 + …..
State the difference between and intrinsic and extrinsic semiconductor?
Intrinsic = pure semiconductor Extrinsic = impurities atoms have been added
What is internal resistance?
Charges passing through a cell meet resistance. A cell therefore has internal resistance.
How do you find the EMF and short circuit current from the graph?
EMF = y intercept
Short circuit current = x intercept
State what is meant by lost volts
Vlost = Ir
The voltage across the internal resistance when a load resistance is connected.
Describe an experiment to find the EMF and internal resistance of a supply.
Adjust variable resistor and take readings of V and I.
Plot a graph of V against I. Gradient of graph = -r.
OR
measure the voltage E when switch open. Close the switch and take a reading of V and I.
Calculate r using E = V + Ir
State the two types of conduction in semiconductors?
Electrons moving in the conduction band Holes moving in the partially filled valence band
State the two types of conduction in semiconductors?
Electrons moving in the conduction band Holes moving in the partially filled valence band
Which equations are used for potential divider circuits?
V1 = (R1/ R1 + R2) x Vs V1/V2 = R1/R2
State what is meant by terminal potential difference (TPD)
Vtpd = E- Ir
The energy per coulomb
transferred by a supply when a load resistance is connected.
How are peak and rms values related?
Vrms = Vpeak/√2
Irms = Ipeak/√2
What is Ohm’s Law?
V=IR
What is forward bias?
Forward biasing means putting a voltage across a diode that allows current to flow easily
• Current flows • Depletion
zone narrows
Describe the band structure of insulators, semiconductors and conductors
The band gap in conductors overlaps. The band gap in semi conductors is small. The band gap in insulators is large.
State what is meant by E - the electromotive force (EMF)
The total amount of energy given to each coulomb of charge by a power supply.
What do the symbols mean? What are their units? Q=It
Q = Charge - measured in coulombs (C)
I = Current - measured in amperes (A)
t = time - measured in seconds (s)
Describe how an n-type semiconductor is formed
A material such as silicon has impurities added with an extra outer electron e.g. Arsenic
How do you find the internal resistance from the graph
The magnitude of the gradient
What is reverse bias?
reverse biasing means putting a voltage across a diode in the opposite direction. The voltage with reverse biasing doesn’t cause any appreciable current to flow. This is useful for changing AC current to DC current.
No current • Depletion
zone widens
Silicon can be doped with arsenic to produce an n-type semiconductor.
State the effect that doping has on the conductivity of silicon.
Increases conductivity.
How do you calculate electrical power?
P = IV = I2R = V2/R
USING RMS VALUES
How do you determine the frequency from an oscilloscope?
T = divisions x timebase frequency = 1/𝑇
Remember: ms = miliseconds
Describe how a p-type semiconductor is formed
A material such as silicon has impurities added with one fewer extra outer electron e.g. Indium
State what is meant by a capacitance of 1F
1F means one coulomb of charge stored per volt
What are the rules for a series circuit?
Is = I1 = I2...... Vs = V1 +V2 + ...... RT = R1 + R2 + ......
Explain what is meant by a photovoltaic effect
- Photons are absorbed when electrons move from the valence band to the conduction band.
- The p-n junction causes the electrons in the conduction band to move towards the n-type semiconductor
- A potential difference is produced across the junction
C = Q/V
What is meant by the symbols
What are their units
C= capacitance(F)
Q= Charge(c)
V=Voltage/Potential Difference(V)
Explain why the reading on the voltmeter decreases when the switch is closed
There is a current flowing when the switch is closed and voltage is lost across the internal resistor.
Which equations do you use to find the energy stored by a capacitor.
E=1/2 QV = 1/2 CV² = 1/2 Q²/C
